"This gearbox is a surprise that it actually works this well for a stock gearbox in a CYMA CM.028 series ak. I've been pushing it with a Tenergy 8.4v 3800mah and it hasn't given up on me yet since the day I've gotten it which was pretty much 2 months ago. Yes, this should fit both CYMA and JG ak's no matter what year it is. I would advice you to reshim the gears just to make sure it is right. The trigger response could do some major work though."